Wouter Schuitemaker, investment director at the Business Birmingham organisation, has even labelled the project "essential" for economic growth in the UK".

But there has been widespread opposition to the plan, not least among Conservative MPs, many of whose Home Counties constituencies would see acres of green land carved up and turned into railway lines.

Labour’s Maria Eagle, who expects extra measures to be announced by the government to protect the Chilterns in the final route, called the changes an “expensive fix”.

She accused the government of “spending hundreds of millions of pounds in tunnelling to save the PM from an embarassing Cabinet resignation.”

It’s not just MPs who are getting het-up over HS2. John Cartwright, Conservative leader of Aylesbury Vale district council in Buckinghamshire says the plans are costing Cameron core support.

“David Cameron is running the risk of losing that traditional support, and he may pay very heavily for it,” he told Huff Post UK.

“I don’t think he realises the actual political effect of going ahead. He will lose seats, he will lose Tory seats, no question about that if it goes ahead. Why would these people vote Conservative?

“Why on earth would they? It will have an effect on councils and on MPs. So much so that if you think about his precarious position at this moment in time with the coalition etc, etc, he couldn’t get a majority last time..

“If he takes 20 Conservative MPs outside and shoots them he won’t get a majority.”

Cartwright says his council is one of the 18 in the so-called ‘51m’ group, a collective of county and district councils, named after the figure they claim HS2 will cost every parliamentary constituency.

The group will meet as soon as the transport secretary announces whether HS2 is getting the go-ahead, to try to fight the decision in a judicial review. He believes the argument will not be won anywhere apart from a court of law.

“I went to a reception at 10 Downing Street at the invitation of the prime minister, who I met. We discussed the different parts of the world we represented and he noted we were fairly close together. I said ‘that’s right’ and he said ‘one thing we’re not going to talk about tonight is HS2’ and I said ‘Sir, you can hide but you can’t avoid the problem.’”

“Let’s put it this way. When the M40 extension was agreed in the mid 1950s it took until the 1980s until it was actually built. Until they actually start laying track I don’t think there’s any certainty it will actually be built. I think that’s all the more reason, given the huge sums involved, one needs to be satisfied that one’s getting good value for the taxpayer. ”

The parliamentary arithmetic is crude. If the decision went to a vote now, the government are likely to win - even if they lack the support of one of their cabinet members. Baldry says there are “at most” 30 MPs from all parties against HS2 and willing to defy a whip.

“I think that the opponents of HS2 are going to have to think very carefully through their tactics about how they deal with this issue at Westminster.

“Organisations such as the Taxpayers’ Alliance who are very concerned about the cost of HS2 and its impact will start flagging up to MPs that this is going to have an impact on their constituencies.

“If it goes ahead the government will have less money than they have at present for infrastructure projects, building hospitals, new schools in their patch.”

As for the campaigners themselves? They’ve vowed not to give up. HS2 Action Alliance director Hilary Wharf pledged that “the opposition will continue to get stronger.”

“Politically it's quite a strange decision for a Tory government to take. But to be fair it's not actually that particular route, the particular point is that it's a waste of money and the wrong priority. The business case itself is completely exaggerated. We don't believe that HS2 can cure the north-south divide.

“We are confident that HS2 will never be built. Look at the third runway at Heathrow. The facts are actually on our side. We will just keep reminding people what the facts are.”

Philip Hammond, the former transport secretary, accused many who opposed the HS2 plans of NIMBYism. But HS2 Action Alliance director Hilary Wharf said: “We are not NIMBYs. I’m an economist. Yes, it does go near me. But there is an economic and environmental case. Ultra high-speed isn’t green.”

HS2: The facts

Who’s for it: It’s an unlikely union between big business, the unions and all three political parties. In fact, at first glance it seems everyone’s for it.
Who’s against it: The Countryside Alliance, the Taxpayers' Alliance, and a handful of MPs.

The benefits: According to a letter by business leaders publish in the Daily Telegraph last week, it will make us rich.

"The absence of a high-speed rail line connecting the northern parts of Britain to London and the European Union is a continuous embarrassment to those promoting British business overseas," they wrote.

The negatives: According to council leader John Cartwright: “It’s destroying my countryside, in a nutshell. It’s absolutely splitting the land that I represent, the area I represent, in half.”

The worst case scenario, according to Tony Baldry MP: “There being a commitment to build HS2 but the actual work not starting because when it comes to the actual time the Treasury turning round and saying ‘terribly sorry, we actually haven’t got the money this year.’”